fix: make RecordBatchIterator Send to support multi-threaded consumers like DuckDB

Author: chitralverma

connectorx-python/src/arrow.rs

@@ -15,7 +15,7 @@ use std::sync::Arc;
 pub struct PyRecordBatch(RecordBatch);
 
 /// Python-exposed iterator over RecordBatches
-#[pyclass(unsendable, module = "connectorx")]
+#[pyclass(module = "connectorx")]
 pub struct PyRecordBatchIterator(Box<dyn RecordBatchIterator>);
 
 #[pymethods]

connectorx/src/arrow_batch_iter.rs

@@ -153,7 +153,7 @@ where
     }
 }
 
-pub trait RecordBatchIterator {
+pub trait RecordBatchIterator: Send {
     fn get_schema(&self) -> (RecordBatch, &[String]);
     fn prepare(&mut self);
     fn next_batch(&mut self) -> Option<RecordBatch>;
@@ -167,7 +167,7 @@ where
         TSD = ArrowStreamTypeSystem,
         S = S,
         D = ArrowStreamDestination,
-    >,
+    >+ std::marker::Send,
 {
     fn get_schema(&self) -> (RecordBatch, &[String]) {
         (self.dst.empty_batch(), self.dst.names())